1. Field of the Invention
The present invention relates to a compressor, and more particularly, to an apparatus for controlling a driving of a reciprocating compressor and a method thereof.
2. Description of the Background Art
Generally, a reciprocating compressor is not provided with a crankshaft for converting a rotary motion into a linear motion thus to have a less frictional loss. Therefore, the reciprocating compressor has more increased compression efficiency than a general compressor.
When the reciprocating compressor is applied to a refrigerator or an air conditioner, a cooling capacity thereof is controlled by varying a compression ratio by varying a stroke voltage inputted thereto. Herein, the stroke denotes a distance between an upper dead point of a piston and a lower dead point.
The conventional reciprocating compressor will be explained with reference to FIG. 1.
FIG. 1 is a block diagram showing a construction of an apparatus for controlling a driving of a reciprocating compressor in accordance with the conventional art.
As shown, the conventional apparatus for controlling a driving of a reciprocating compressor comprises a current detector 4 for detecting a current applied to a motor (not shown) of a reciprocating compressor 6, a voltage detector 3 for detecting a voltage applied to the motor, a stroke calculator 5 for calculating a stroke estimation value of the compressor according to the detected current and voltage and a parameter of the motor, a comparator 1 for comparing the calculated stroke estimation value with a preset stroke command value and thus outputting a difference value therebetween, and a stroke controller 2 for controlling a stroke of the compressor 6 by varying a voltage applied to the motor by controlling a turn-on cycle of a triac (not shown) connected to the motor in serial according to the difference value.
Hereinafter, an operation of the apparatus for controlling a driving of the reciprocating compressor according to the present invention will be explained with reference to FIG. 1.
The current detector 4 detects a current applied to a motor (not shown) of the compressor 6, and outputs the detected current value to the stroke calculator 5. The voltage detector 3 detects a voltage applied to the motor, and outputs the detected voltage value to the stroke calculator 5.
The stroke calculator 5 calculates a stroke estimation value (X) of the compressor by substituting the detected current value, the detected voltage value, and a parameter of the motor into the following formula 1, and then applies the calculated stroke estimation value (X) to the comparator 1.
                    X        =                              1            α                    ⁢                      ∫                                          (                                                      V                    m                                    -                  Ri                  -                  Li                                )                            ⁢                              ⅆ                t                                                                        formula        ⁢                                  ⁢        1            
Herein, the R denotes a resistance value, the L denotes a motor inductance value, the α denotes a motor constant, the Vm denotes a voltage applied to the motor, the i denotes a current applied to the motor, and the ī denotes a variation ratio of a current applied to the motor according to time. That is, the ī denotes a differential value of the i (di/dt).
Then, the comparator 1 compares the stroke estimation value with the stroke command value, and applies a difference value therebetween to the stroke controller 2.
The stroke controller 2 varies a voltage applied to the motor of the compressor 6 according to the difference value, thereby controlling a stroke of the compressor 6.
FIG. 2 is a flowchart showing a method for controlling a driving of a reciprocating compressor in accordance with the conventional art.
When a stroke estimation value obtained by the stroke calculator 5 is applied to the comparator 1 (S1), the comparator 1 compares the stroke estimation value with a preset stroke command value thereby to obtain a difference value therebetween (S2). Then, the comparator 1 outputs the difference value to the stroke controller 2.
When the stroke estimation value is less than the stroke command value, the stroke controller 2 increases a voltage to be applied to the motor in order to control a stroke of the compressor (S3). On the contrary, when the stroke estimation value is greater than the stroke command value, the stroke controller 2 decreases a voltage to be applied to the motor (S4). Herein, the stroke controller 2 increases or decreases a voltage to be applied to the motor by controlling a turn-on cycle of a triac (not shown) electrically connected to the motor.
The stroke command value is varied according to a size of a load of the reciprocating compressor. That is, when the load of the reciprocating compressor is large, the stroke command value is increased not to decrease a stroke of a piston thereby to prevent a cooling capacity from being decreased. On the contrary, when the load of the reciprocating compressor is small, the stroke command value is decreased not to increase a stroke of a piston thereby to prevent a cooling capacity from being increased and to prevent a collision between the piston and a cylinder due to an over stroke.
The conventional linear compressor using a stroke voltage has a decreased efficiency when a stroke of a piston is decreased into a certain level, thereby having a limitation in implementing a capacity variation.
The conventional rotary compressor using a rotation motor implements a capacity variation of a wide range by varying a frequency. When a frequency is varied within a range of a small capacity variation, the efficiency of the rotary compressor is not drastically decreased. On the contrary, when a stroke of a piston is small, the efficiency of the reciprocating compressor is decreased.